Olefins are traditionally produced from petroleum feedstock by catalytic or steam cracking processes. These cracking processes, especially steam cracking, produce light olefin(s) such as ethylene and/or propylene from a variety of hydrocarbon feedstock. Ethylene and propylene are important commodity petrochemicals useful in many processes for making plastics and other chemical compounds. Ethylene is used to make various polyethylene plastics, and in making other chemicals such as vinyl chloride, ethylene oxide, ethylbenzene and alcohol. Propylene is used to make various polypropylene plastics, and in making other chemicals such as acrylonitrile and propylene oxide.
The petrochemical industry has known for some time that oxygenates, especially alcohols, are convertible into light olefin(s). The preferred oxygenate for light olefin production is methanol. The process of converting methanol-to-olefins is called the methanol-to-olefin(s) process. There are numerous technologies available for producing oxygenates, and particularly methanol, including fermentation or reaction of synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials including coal, recycled plastics, municipal waste or any other organic material. Generally, the production of synthesis gas involves a combustion reaction of natural gas, mostly methane, and an oxygen source into hydrogen, carbon monoxide and/or carbon dioxide. Syngas production processes are well known, and include conventional steam reforming, autothermal reforming or a combination thereof.
Syngas is then processed into methanol. Specifically, the components of syngas (i.e., hydrogen, carbon monoxide and/or carbon dioxide) are catalytically reacted in a methanol reactor in the presence of a heterogeneous catalyst. For example, in one process, methanol is produced using a copper/zinc oxide catalyst in a water-cooled tubular methanol reactor.
The methanol-to-olefins reaction is highly exothermic. Moreover, this reaction has a large amount of water. Water comprises as much as one half of the total weight of the effluent stream to isolate the olefins the effluent stream. Consequently, the water must be removed by condensation in a quench device to isolate the olefin product. The quench device cools the effluent stream to the condensation temperature of water. Quenching the product recovers large quantity of water at the temperature near the boiling point of the quench medium. It is desirable to recover heat in higher temperature streams before quenching.
U.S. Pat. No. 6,121,504 describes a quench apparatus for an oxygenate to olefins process as well as a process for using the quench apparatus. The process removes water from the effluent stream as well as some oxygenate feedstock such as methanol.
U.S. Pat. No. 6,403,854 describes a two stage solids wash and quench for use with the oxygenate conversion process. This reference shows that catalyst fines are removed through a first quench stage. Water and methanol is removed in a second quench stage.
It would be desirable to have a quench tower that effectively disposes catalyst fines, removes water and removes oxygenates in an effective and efficient way. The present invention satisfies these and other needs.